A comparative analysis of structural and luminescent properties of homoepitaxially and quasi-homoepitaxially grown LuAG:Ce single crystalline films under ambient and high pressure

This work is dedicated to investigating the structural, luminescence and photocurrent characteristics of LuAG:Ce single crystalline films (SCFs) grown using the Liquid Phase Epitaxy method on both LuAG and YAG substrates. The primary objective is to analyze the influence of different growth modes, namely homoepitaxial (HE) and quasi-homoepitaxial (QHE), on the structural and luminescent properties of Ce3+ ions under ambient and high-pressure conditions. Based on the results of XRD measurements, we can conclude that both epitaxial structures are fully relaxed. However, a slight deformation of the garnet lattices is observed, manifesting the inequality of the in-plane and out-of-plane lattice constants of substrates and films. The difference in the energy gap values between positions of 4f-5d1,2 Ce3+ absorption bands (6-12 meV) and the positions of Ce3+ emission band (6 meV) was observed for both LuAG:Ce films and caused by the small differences in local perturbations of garnet hosts for epitaxial structures, grown in HE and QHE modes. The Ce3+ emission intensity in LuAG:Ce HE and QHE films decreases with temperature in the 10-300 K range. The decay time of the Ce3+ luminescence in LuAG:Ce HE film demonstrates a weak temperature dependence in the mentioned range. However, in LuAG:Ce QHE grown film, the decay time of the Ce3+ emission shows notable temperature dependences in the 10-300 K range, probably due to the formation of Ce4+-Pb2+ pair centers. The non-monotonical redshift of the Ce3+ emission band and the increse of the Ce3+ decay time are observed in both LuAG:Ce HE and QHE films under increasing external pressure from ambient to 19 GPa due to the compression and distortion of the crystal lattice. The redshift changes of the Ce3+ emission band on pressure are significantly more complicated for LuAG:Ce QHE-grown film than their HE counterpart. The outcomes of this study contribute to the fundamental understanding of epitaxial growth processes and their impact on the luminescence characteristics of rare-earth-doped materials in single crystalline film form.